Currently, as the popularity and development of electronic devices, such as a digital camera, and a scanner, etc., digital images are so easy to be obtained. However, any entity sensors (such as a thermal sensor, electric sensor, or other types of sensors) are subjected to noise, which affects genuineness of signal measurement. Thus, any obtained image data contain signals and noise. Various applications related to images, such as medical image analysis, image segment, and object detection, etc., usually require an effective noise suppression method to further obtain a reliable result. Hence, image filtering has become one of most important and wide study subjects in image processing and computer vision. A gray image is one of important and widely-used image types, and its noise suppression method is crucial. However, existing filtering methods will make edges of an image look unnatural, and straight edges possibly look rough.
It should be noted that the above description of the background art is merely provided for clear and complete explanation of the present invention and for easy understanding by those skilled in the art. And it should not be understood that the above technical solution is known to those skilled in the art as it is described in the background art of the present invention.